Phonon temperature, acoustic

The effect of device temperature on the electrical behavior of the device occurs due to the lattice temperature dependence of the electron scattering rate. When the LO phonon and acoustic phonon temperatures rise, the electron scattering rate increases, thus increasing the electrical resistance or decreasing the carrier mobility. The coupling of electrical and thermal characteristics suggest that these must be analyzed concurrently. 

In addition to the photoluminescence red shifts, broadening of photoluminescence spectra and decrease in the photoluminescence quantum efficiency are reported with increasing temperature. The spectral broadening is due to scattering by coupling of excitons with acoustic and LO phonons [22]. The decrease in the photoluminescence quantum efficiency is due to non-radiative relaxation from the thermally activated state. The Stark effect also produces photoluminescence spectral shifts in CdSe quantum dots [23]. Large red shifts up to 75 meV are reported in the photoluminescence spectra of CdSe quantum dots under an applied electric field of 350 kVcm . Here, the applied electric field decreases or cancels a component in the excited state dipole that is parallel to the applied field the excited state dipole is contributed by the charge carriers present on the surface of the quantum dots. 

Bulk silicon is a semiconductor with an indirect band structure, as schematically shown in Fig. 7.12 c. The top of the VB is located at the center of the Brillouin zone, while the CB has six minima at the equivalent (100) directions. The only allowed optical transition is a vertical transition of a photon with a subsequent electron-phonon scattering process which is needed to conserve the crystal momentum, as indicated by arrows in Fig. 7.12 c. The relevant phonon modes include transverse optical phonons (TO 56 meV), longitudinal optical phonons (LO 53.5 meV) and transverse acoustic phonons (TA 18.7 meV). At very low temperature a splitting (2.5 meV) of the main free exciton line in TO and LO replicas can be observed [Kol5]. 

Here we are interested in the low temperature behavior of the ZPL if the excited state is close to dynamical instability. We must account for the acoustic phonons. First we consider the limiting case w = wCI. Taking into account that, with account of the acoustic phonons, for small co Re(G([Pg.144]

By comparing the resonance frequency Eq.(ll) and the phonon vibration frequency Eq.(12), we see that they are almost the same, 0.3 0.4 x 1014 s 1. This affirms the possibility of a spin-paired covalent-bonded electronic charge transfer. For vibrations in a linear crystal there are certainly low frequency acoustic vibrations in addition to the high frequency anti-symmetric vibrations which correspond to optical modes. Thus, there are other possibilities for refinement. In spite of the crudeness of the model, this sample calculation also gives a reasonable transition temperature, TR-B of 145 °K, as well as a reasonable cooperative electronic resonance and phonon vibration effect, to v. Consequently, it is shown that the possible existence of a COVALON conduction as suggested here is reasonable and lays a foundation for completing the story of superconductivity as described in the following. 

Because the phonon vibration frequency, o, is visible only when all other higher order of phonon vibration (whether be acoustic or optical) are harnessed, Covalon conduction must be a low temperature phenomenon. 

The quite another temperature dependence of the rate constant at helium temperatures is resulted in the case when the principal contribution to dispersion a in formula (25a) gives the acoustic phonons. Their frequencies lie in the interval [0, lud], where tuD is Debye s frequency. Even if hin0 kT, it exists always in the range of such low frequencies that haxkT. It is these phonons that give the contribution depending on the temperature in the dispersion a [15], One assumes that the displacements of the equilibrium positions of phonon modes Sqs do not depend on frequency. Then, the calculation of the rate constant gives at low temperatures, hcou>kT,... 

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